Thanks Cheizz for your contributions. I had seen that video comparing fins in the pool but forgotten about it. Since the new fins should be as powerful as possible the X-streams are out. I already have the Tusas and like I said they are comfortable, easy on the legs, good for maneuvering and superb in quality. No need for a second pair of "nice enough" fins.
I actually got a tape measure and used it on my main travel cases. Turns out I can stretch up to about 68-69 cm. Which fits - even if by a small margin. Regular Quattros+ are said to be 65 cm overall
here and
here.
I am much drawn towards the Quattros given their reputation, choice of colors and (why not) price - they cost about half the Supernovas price in Europe.
While researching the Avantis I found about the Excite and Excite Pros. Supposedly they should have even better propulsion. But then I found that they have this
"flutter click" issue. Having experienced that myself with other fins I know it's quite annoying, even if benign. So the Excites too are out.
Which leaves the RK3s. I found a few opinions describing them as very powerful, but no conclusive direct comparison with the Quattros. Will keep looking.